This application is based on application No. H10-212635 filed in Japan on Jul. 28, 1998, the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a device such as a digital camera, and particularly to a device having a display for displaying an image. The invention relates to a device powered by an external/internal power source.
2. Description of the Prior Art
Many digital cameras are provided with a display unit such as a backlit LCD (liquid crystal display) so as to allow viewing of a live image during shooting and viewing of a recorded image after shooting. Since digital cameras are typically carried around as they are used, most digital cameras use a battery as a source of electric power they require to operate.
However, the capacity of batteries available today is insufficient to meet the power consumption of digital cameras for many hours. Accordingly, when a digital camera is used in a situation where portability is not required such as when it is used in a state connected to a personal computer, an external power source such as an AC adapter is used. Moreover, to alleviate depletion of a battery as much as possible, digital cameras are usually provided with a function of, when no operation is performed for a predetermined length of time, shutting off supply of electric power to at least part of its display unit including an LCD and a video circuit, or a function of, in such a situation, shutting off supply of electric power to the entire digital camera. In the present specification, the former function will be referred to as the automatic-monitor-off function and the latter function as the automatic-power-off function.
Note that the automatic-power-off function may be achieved by cutting off an electric power supply path in such a way that supply of electric power is restarted only when the path is closed again directly by mechanical operation of a switch, or by bringing a camera into a so-called sleep state, i.e. a stand-by state in which its controller itself is kept in operation and waits for entry of a command that requests starting of a switching device such as a transistor by which an electric power supply path from a power source is opened or closed.
However, some conventional digital cameras are so designed that the automatic-power-off function is maintained even when they are operating on electric power fed from an external power source. With such digital cameras, even in a situation where the use of an external power source eliminates the risk of battery depletion, their operation may be suddenly interrupted in the middle of their use as a result of supply of electric power being shut off automatically. On the other hand, some other conventional digital cameras are so designed that the automatic-power-off function is disabled when they are operating on electric power fed from an external power source. With such digital cameras, although such interruption of operation as mentioned above can be avoided, their display unit may be damaged by overheating as a result of being kept energized for long hours.
An object of the present invention is to provide a device that ensures alleviated depletion of a built-in battery and that offers enhanced user-friendliness and safety when operating from an external power source.
To achieve the above object, according to one aspect of the present invention, a device that operates from an internal power source or from an external power source is provided with: a display unit for displaying an image; and a controller that counts the time that has elapsed after execution of a predetermined operation so that, if the device is operating from the internal power source, operation of the entire device is ended when a predetermined length of time has been counted and, if the device is operating from the external power source, operation of the display unit is ended but operation of the other portions of the device is continued when a predetermined length of time has been counted.
According to another aspect of the present invention, a device that operates from an internal power source or from an external power source is provided with: a display unit for displaying an image; and a controller that, when no operation has been performed for a predetermined length of time, ends operation of the entire device, if the device is operating from the internal power source, and ends operation of the display unit but continues operation of the other portions of the device, if the device is operating from the external power source.
According to still another aspect of the present invention, a device that operates from an internal power source or from an external power source is provided with: a display unit for displaying an image; and a controller that, when no operation has been performed for a first predetermined length of time, ends operation of the display unit and, when no operation has been performed for a second predetermined length of time that is longer than the first predetermined length of time, ends operation of the entire device only if the device is operating from the internal power source.